Static Compressive Stress Research Articles

A large magnetic-field-induced strain in Ni–Fe–Mn–Ga–Co ferromagnetic shape memory alloy

Abstract To obtain a large strain of Ni–Fe–Ga–Co ferromagnetic shape memory alloys, the effects of Mn on the magnetocrystalline anisotropy constant Ku, and the magnetic-field-induced strain (MFIS) under static stresses were investigated. The value of Ku was increased by the addition of Mn, and Ni49.5Fe14.5Mn4.0Ga26.0Co6.0 alloy was accompanied by a relatively large value of −1.5 × 105 J/m3 at room temperature. From the stress–strain curves of this alloy, the twinning stress is estimated to be 8–10 MPa. Consequently, the Ni49.5Fe14.5Mn4.0Ga26.0Co6.0 alloy provides a large MFIS of about 11.3% at room temperature under a static compressive stress of about 8 MPa.

Energetic optimization of a piezo-based touch-operated button for man–machine interfaces

This paper discusses the optimization of a touch-operated button for man–machine interfaces based on piezoelectric energy harvesting techniques. In the mechanical button, a common piezoelectric diaphragm, is assembled to harvest the ambient energy from the source, i.e. the operator’s touch. Under touch force load, the integrated diaphragm will have a bending deformation. Then, its mechanical strain is converted into the required electrical energy by means of the piezoelectric effect presented to the diaphragm. Structural design (i) makes the piezoceramic work under static compressive stress instead of static or dynamic tensile stress, (ii) achieves a satisfactory stress level and (iii) provides the diaphragm and the button with a fatigue lifetime in excess of millions of touch operations. To improve the button’s function, the effect of some key properties consisting of dimension, boundary condition and load condition on electrical behavior of the piezoelectric diaphragm are evaluated by electromechanical coupling analysis in ANSYS. The finite element analysis (FEA) results indicate that the modification of these properties could enhance the diaphragm significantly. Based on the key properties’ different contributions to the improvement of the diaphragm’s electrical energy output, they are incorporated into the piezoelectric diaphragm’s redesign or the structural design of the piezo-based button. The comparison of the original structure and the optimal result shows that electrical energy stored in the diaphragm and the voltage output are increased by 1576% and 120%, respectively, and the volume of the piezoceramic is reduced to 33.6%. These results will be adopted to update the design of the self-powered button, thus enabling a large decrease of energy consumption and lifetime cost of the MMI.

DESIGNING OF A TESTING MACHINE FOR SHEAR-MODE FATIGUE CRACK GROWTH

As recognized, flaking-type failure is one of the serious problems for railroad tracks and bearings. In essence, flaking-type failure is closely related to the growth of the shear-mode (Mode-II and Mode-III) fatigue crack. In our research group, it is demonstrated that a shear-mode fatigue crack can be reproduced for cylindrical specimens by applying the cyclic torsion in the presence of the static axial compressive stress. However, a biaxial servo-hydraulic fatigue testing machine is quite expensive to purchase and costly to maintain. The low testing speed (about 10Hz) of the testing machine further aggravates the situation. As a result, study on shear-mode fatigue crack growth is still in the nascent stage. To overcome the difficulties mentioned above, in this research activity, we developed a high-performance and cost-effective testing machine to reproduce the shear-mode fatigue crack growth by improving the available resonance-type torsion fatigue testing machine. The primary advantage of using the resonance-type torsion fatigue testing machine is cost-efficiency. In addition, the testing speed effectively can be improved, in comparison with that of a biaxial servo-hydraulic fatigue testing machine. By utilizing the newly-designed testing machine, we have demonstrated that we can successfully reproduce the shear-mode fatigue crack.

Effects of Crack Size and Crack Face Interference on Shear Fatigue Crack Growth in a Bearing Steel

The near-threshold fatigue behavior of small, semi-elliptical surface cracks in a bearing steel was investigated under cyclic shear-mode loading in ambient air. Fully-reversed cyclic torsion was combined with a static axial compressive stress to obtain a stable shear-mode crack growth in the longitudinal direction of cylindrical specimens. Shear stress amplitude was gradually decreased with an increase in crack length and the crack finally became non-propagating. Abrasive wear on the crack faces was inferred by debris and also by changes in microstructure in the wake of crack tip. Further, it was found that these effects resulted in a significant decrease in the crack growth rate. In this study, we shed light on the important role of the crack size and crack face interference on the crack growth behavior.

OS0711 せん断モード疲労き裂進展試験について(OS7-2 解析・評価・き裂I,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

It is recognized that flaking-type failure due to contact fatigue is closely related to the growth of the shear-mode (Modes II and III) fatigue crack. In our research group, it is demonstrated that a shear mode fatigue crack can be reproduced for the cylindrical specimens by applying the cyclic torsion in the presence of the static axial compressive stress. However, a biaxial servo-hydraulic fatigue testing machine used is quite expensive to purchase and costly to maintain. Low testing speed (〜10 Hz) of the testing machine further aggravates the situation. As a result, study on shear mode fatigue crack growth is still in nascent stage. To overcome those difficulties, we have developed a high performance and cost-effective testing machine to reproduce the shear mode fatigue crack growth by improving the available resonance-type torsion fatigue testing machine. The primary advantage of using the resonance-type torsion fatigue testing machine is cost-efficiency. In addition, the testing speed can be effectively improved in comparison with that of a biaxial servo-hydraulic fatigue testing machine.

Shear mode threshold for a small fatigue crack in a bearing steel

The fatigue behaviour of small, semi-elliptical surface cracks in a bearing steel was investigated under cyclic shear-mode loading in ambient air. Fully reversed torsion was combined with a static axial compressive stress to obtain a stable shear-mode crack growth in the longitudinal direction of cylindrical specimens. Non-propagating cracks less than 1 mm in size were obtained (i) by decreasing the stress amplitude in tests using notched specimens and (ii) by using smooth specimens in constant stress amplitude tests. The threshold stress intensity factor ranges, ΔKIIth and ΔKIIIth, were estimated from the shape and dimensions of non-propagating cracks. Wear on the crack faces was inferred by debris and also by changes in microstructure in the wake of crack tip. These effects resulted in a significant increase in the threshold value. The threshold value decreased with a decrease in crack size. No significant difference was observed between the values of ΔKIIth and ΔKIIIth.

The influence of constant axial compression pre-stress on the fatigue failure of torsion loaded tube springs

This paper reports the results of a series of biaxial static compression and torsion experiments performed to evaluate the effects of static compression stress on the fatigue life those smooth tubes made of high strength spring steel. Compression pre-stress was introduced by a solid steel bar inserted into a hollow spring and loaded with a screw-joint. The experimentally obtained results show a significant extension of fatigue strain life as a result of combining axial compression loading with torsion. Cracking behavior was observed and it was noted that compression pre-stresses contribute to retardation of the fatigue crack initiation process and, consequently, contribute to the extension of fatigue life. The fatigue shear crack initiated in a transverse direction. This crack continues to propagate in the same direction until it starts to propagate as a macro-crack on the maximum shear plane.

Large magnetic-field-induced strain in Co–Ni–Al single-variant ferromagnetic shape memory alloy

At room temperature, Co41Ni32Al27 single-variant ferromagnetic shape memory alloy with a uniaxial magnetic anisotropy constant of –2.0 × 106 erg cm–3 exhibits a large magnetic-field-induced strain of 3.3% under a static compressive stress of about 10 MPa applied along the hard magnetization direction of the c-axis (c/a > 1). Compared with data for other alloys, it becomes clear that a small change in twinning stress in the stress–strain curve is necessary for a large strain.

Synchrotron X-ray diffraction study of load partitioning during elastic deformation of bovine dentin

The elastic properties of dentin, a biological composite consisting of stiff hydroxyapatite (HAP) nano-platelets within a compliant collagen matrix, are determined by the volume fraction of these two phases and the load transfer between them. We have measured the elastic strains in situ within the HAP phase of bovine dentine by high energy X-ray diffraction for a series of static compressive stresses at ambient temperature. The apparent HAP elastic modulus (ratio of applied stress to elastic HAP strain) was found to be 18 ± 2 GPa. This value is significantly lower than the value of 44 GPa predicted by the lower bound load transfer Voigt model, using HAP and collagen volume fractions determined by thermo-gravimetric analysis. This discrepancy is explained by (i) a reduction in the intrinsic Young’s modulus of the nano-size HAP platelets due to the high fraction of interfacial volume and (ii) an increase in local stresses due to stress concentration around the dentin tubules.

Effect of uniaxial stress on the electromechanical properties in ferroelectric thin films under combined loadings

The electromechanical properties of ferroelectric thin films under an alternating electric field and a static uniaxial compressive stress are investigated using the modified planar four-state Potts model. To implement the electromechanical properties and the coupling of the electrical and mechanical response, the mechanical energy density as well as the energy due to anisotropic switching between a-domain and c-domain are incorporated in the Hamiltonian. Besides, there are two contributions to the strain at each cell: eigenstrain and elastic strain. Our simulation results show that the longitudinal strain-electric field butterfly loop shifts downward along strain axis and that for the transverse strain shifts upward as the stress magnitude is increased. Moreover, the polarization-electric field hysteresis loop becomes a double-loop under a large compressive stress. The piezoelectric coefficient increases with the stress magnitude and reaches a maximum value at a critical stress level. It then gradually decreases to a small value at large stress magnitudes. Our results qualitatively agree with experimental ones.

Whole-body vibration exposure experienced by motorcycle riders – An evaluation according to ISO 2631-1 and ISO 2631-5 standards

Riders of twelve motorcycles, comprising 6 full-scale motorbikes and 6 motor-scooters, and 5 sedan vehicles, performed test runs on a 20.6 km paved road composed of 5 km, 5 km, and 10.6 km of rural, provincial and urban routes, respectively. Each test run of motorcycle was separately performed under speed limits of 55 km/h and 40 km/h. Tri-axial accelerations of whole-body vibration (WBV) were obtained by using a seat pad and a portable data logger, and the driver's view was videotaped with a portable media recorder. Root mean square ( RMS) acceleration, 8-h estimated vibration dose value ( VDV (8)) and 8-h estimated daily dose of static compression dose ( S ed ) were determined from the collected data in accordance with ISO 2631-1 and ISO 2631-5 standards. Experimental results indicate that the WBV values of the sedan vehicle drivers have low RMS, VDV (8) and S ed values ( RMS 0.27–0.32 m/s 2; VDV (8) 6.3–8.3 m/s 1.75; S ed 0.21–0.26 MPa). However, over 90% of the motorcycle riders had VDV (8) (mean 23.5 m/s 1.75) exceeding the upper boundary of health guidance caution zone (17 m/s 1.75) recommended by ISO 2631-1, or had S ed (mean 1.17 MPa) exceeding the value associated with a high probability of adverse health effects (0.8 MPa) recommended by ISO 2631-5. Over 50% of the motorcycle riders reached these boundary values for VDV and S e in less than 2 h. The WBV exposure levels of the full-scale motorbikes riders and motor-scooter riders were not significantly different. However, the RMS and VDV (8) values of motorcycle riders indicate significant roadway effect ( p < 0.001), while their S ed values indicate significant speed limit effect ( p < 0.05). This study concludes that the WBV exposure levels of common motorcycle riders are distinctively higher than those of sedans, even on a regular paved road. The impact on health of WBV exposure in motorcycle riders should be carefully addressed with reference to ISO 2631-1 and ISO 2631-5. Relevance to industry This study compares the predicted health risks of motorcycle riders according to ISO 2631-1 and ISO 2631-5 standards. Experimental data suggest that the vibration dose value of ISO 2631-1 and daily dose of equivalent static compression stress of ISO 2631-5 have roughly equivalent boundaries for probable health effects.

Effect of hydrogen on Mode II fatigue crack behavior of tempered bearing steel and microstructural changes

In order to clarify the effect of hydrogen on Mode II fatigue behavior, fatigue tests on a bearing steel (SAE52100, HV = 748) were conducted. Cyclic torsion both with and without a static axial compressive stress was applied to hydrogen-precharged and uncharged specimens. For both loading cases, fatigue lives were shorter for the hydrogen-precharged specimens than for the uncharged specimens. Mode II and Mode I fatigue crack growth rates in the hydrogen-precharged specimens were higher than those in the uncharged specimens. The density of Mode II fatigue cracks near the end of life ( N/ N f = 0.97) was greater in the hydrogen-precharged specimen than in the uncharged specimen. Microstructural changes and an increased density of slip bands were formed only in the hydrogen-precharged specimens. From these observations, it is hypothesized that hydrogen enhances slip deformation and localized slip bands thus increasing the density of cracks in the hydrogen-precharged specimens.

Damage Evaluation of Piezoelectric Ceramics from the Variation of the Elastic Coefficient under Static Compressive Stress

In the present article, columnar specimens of lead zirconate titanate (PZT) were subjected to static compressive stress, and the characteristics of fracture under compression were clarified. The fracture tests were interrupted at certain intervals, and resonance and anti-resonance frequencies and electrostatic capacity were measured by means of an impedance analyzer with the compressive stress unloaded. The interruption and measurement were repeated with the maximum stress increased up to the fracture. The material properties of the specimens such as the electromechanical coupling coefficient, the dielectric constant, the elastic coefficient, and the piezoelectric constant were evaluated based on the resonant properties, and the variation of the material properties in the process of the fracture were clarified experimentally. An elastic coefficient was also evaluated from stress— strain relations during the compression fracture tests, and the difference in the elastic coefficient depending on the method of evaluation was discussed. Furthermore, internal damage developed in the specimens during the compression fracture tests was evaluated based on the variation of the elastic coefficients indirectly as a scalar damage variable on the basis of the continuum damage mechanics. Features of the damage development and the dependence of the quantitative value of the damage variables on the evaluation method of the elastic coefficient were discussed. SEM micrographs of the fracture surface were observed and the causes of the damage were investigated.

A Critical Compressive Stress for Increasing the Oxidation Kinetics of Fe–20Cr Alloy Oxidized at 900 °C

The effects of compressive stresses on the oxide-scale morphologies formed on an Fe–20Cr alloy were investigated by comparison of the oxidation behavior in air under classical conditions, i.e., without any applied mechanical stresses and under static compressive stresses, at 900 °C. The study was carried out mainly by comparisons of oxidation kinetics gained by thermogravimetric analysis (TGA), surface morphologies of oxidized specimens observed by scanning electron microscopy (SEM), oxidized products examined by X-ray diffraction (XRD). It was found that the application of compressive stresses induced an increase in oxidation rate, but a decrease of oxide grain size. When the stresses are in the range of 5–8 MPa, both chromium- and iron-oxides formed but, at other stresses, only chromia was present. In particular, there was a maximum in oxidation rate when the applied stress was 5 MPa. The paper places emphasis on analyzing the cause of this phenomenon.

Modelling the compression strength of polymer laminates in fire

A theoretical and experimental study is presented into the thermal decomposition, softening and failure of polymer matrix laminates under combined compressive loading and one-sided heating to high temperature. A thermo-mechanical model is presented for predicting the time-to-failure of laminates supporting a static compressive stress during one-sided heating. The thermal component of the model predicts the mass loss due to polymer decomposition and through-thickness temperature profile of the hot laminate. The mass loss and temperature predictions are validated against measured data, and the agreement is good. The thermal analysis is coupled to a mechanics-based model that calculates the loss in compressive strength with increasing temperature. The model can also predict the time-to-failure of the hot laminate supporting a static compressive load. The accuracy of the model is evaluated using failure times measured in fire-under-compression load tests on a woven E-glass/vinyl ester laminate. The experimental time-to-failure values decreased with increasing heat flux (temperature) and applied compressive stress, and the model can accurately predict these failure times. The paper also examines the dimensional expansion, out-of-plane distortion and failure mechanism of laminates under combined compressive loading and heating. It is envisaged that the thermo-mechanical model is a useful tool to estimate the failure time of compressively loaded composite structures exposed to high temperature or fire.

Stress-assisted magnetic-field-induced strain in Ni–Fe–Ga–Co ferromagnetic shape memory alloys

To obtain a large strain for Ni–Fe–Ga ferromagnetic shape memory alloys, the Curie temperature was increased by adding Co, and the magnetic-field-induced strain (MFIS) has been investigated under static stresses. The magnetocrystalline anisotropy constant K is increased by the addition of Co, and Ni49Fe18Ga27Co6 alloy gives a relatively large value of 1.15×106erg∕cm3 at 300K. From the stress-strain curves for this alloy, the twinning stress is estimated to be 8–9MPa. Consequently, the Ni49Fe18Ga27Co6 alloy exhibits a large MFIS of about 8.5% at room temperature under a static compressive stress of about 8MPa.

Observations on fatigue crack paths in the corners of cold-formed high-strength steel tubes

Fatigue crack propagation in cold-formed corners of high-strength structural steel plate-type structures has been investigated. Large- and small-scale test specimens having complex residual stress states and subject to multi-axial cyclic local stresses have been investigated using both laboratory tests and numerical simulations. The combinations of alternating bending stress, alternating shear stress and static mean stress producing complex multi-axial stress states have been found to influence the fatigue crack path behaviour. Straight, zig-zag and “S” shaped cracks were observed depending on the material strength, range of cyclic loading, residual stress field and multi-axiality of the local stresses. Numerical simulations of residual stresses and linear elastic fracture mechanics were used to help understand the alternate crack paths. Mode I cracks propagating into a static compressive stress field did not arrest, but, due to the multi-axial stresses, combinations of mixed mode I, II and III crack growth with distinct paths were observed. The crack paths depend on the type and range of cyclic loading, material properties and residual stress conditions of the specimens.

Zastosowanie komputerowej analizy obrazu do oceny struktur polimerow wzmacnianych

The images of microstructures of polymer composites; polyamide 6 (PA 6) and polyacetal (POM) reinforced with glass fiber as well as polytetrafluoroethylene (PTFE) filled with bronze (CuSn) powder were the subjects of computer-aided analyses. The computer method used based on quantitative evaluation of composite microstructure as a result of the following parameters' determinations: filler part, dimensions and positions of rectangles described onto the particles (Fig. la), the longest chords of particles (Fig. 1b) and average surfaces of zones of influence (Fig. 1c). The proposed way of analysis has been applied to evaluate the effects of mechanical interactions on the microstructures of composites investigated. These interactions were as follows: POM samples (Fig. 4 and 5) and PA 6 samples (Fig. 6) were subjected to dynamic tensile stress while PTFE samples were subjected to dynamic and static compressive stress (Fig. 3). It was found, between others, that long-lasting fatigue load causes increase in average number of filler particles. The method discussed allows evaluating quantitatively the areas of brittle cracking.

Room-temperature creep of soft PZT under static electrical and compressive stress loading

This study focuses on the experimental investigation of time-dependent effects of a commercial piezoceramic material at room temperature. Specimens in the unpoled or poled state were subjected to an electric field or a compressive stress loading increasing from zero and then kept constant at a certain level. Due to ferroelectric or ferroelastic domain switching, significant nonlinearity and hysteresis were observed in the overall polarisation and strain response. In particular, the material exhibited a creep behaviour as the external loads applied were kept constant for extended periods of time. This creep was of the primary type and could be quantified approximately using the Andrade power law. For an initially unpoled specimen, most pronounced electrical creep was observed when holding the field close to the coercive field. Under purely mechanical loading, the material exhibited the greatest time-dependent effects at a stress level near the coercive stress.

4056 SUJ2におけるせん断型疲労き裂進展(G03-12 き裂進展(1),G03 材料力学)

Growth behaviour of shear-type fatigue crack in a bearing steel, JIS SUJ2, was investigated by a biaxial fatigue testing machine using round specimens. Either following two kinds of defect with total length 400〜440μm and depth 200-300μm was introduced into specimen surface ; (1) a semi-elliptical pre-crack emanating from a 2-hole defect by a tension-compression loading, (2) a 3-hole defect oriented in the axial direction which has FIB slits at the edge of the defect. Fully reversed torsion corresponding to shearing stress amplitude at specimen surface, τ_a=600MPa, was applied to each specimen under static compressive stress σ_m=-1000〜-1200MPa. In case of defect (1), a shear-type crack propagated from the pre-crack in direction perpendicular to the specimen axis. At the specimen surface, the shear-type crack periodically branched from the crack tip and propagated 5〜10μm in Mode I directions. The shear-type crack growth was decelerated with the increase in the crack length and finally stopped at N&cong;7.5×10^6 cycles and 2a&cong;600μm. On the other hand, in case of defect (2), the shear-type crack propagated in axial direction, and the crack growth was accelerated with the increase in the crack length. These results revealed that friction between crack faces is a strong resistance in the shear-type crack growth.